1. Field of the Invention
The present invention relates to a stator sub-assembly, a stator assembly, a motor using the same, and a manufacturing method of the stator assembly.
2. Description of the Related Art
A stepping motor has been extensively used as a motor used for a rotating component and the like of an OA apparatus or an automobile. The stepping motor converts a digital electric input into a mechanical motion in response to electric signals and rotates stepwise by a fixed angle for each step, thus attaining a high accuracy in positioning. One type of such a stepping motor is a PM (permanent magnet) stepping motor using a permanent magnet in a rotor section thereof.
A conventional PM stepping motor is provided with a stator assembly 100 as shown in FIG. 10. The stator assembly 100 comprises two stator subassemblies 101 and 101 attached back to back.
FIG. 11 shows an exploded view of one of the two stator subassemblies 101 and 101. The stator sub-assembly 101 comprises a cylindrical cup-shaped outer stator yoke 102, an inner stator yoke 103 made of a ring-shaped steel plate and a winding 104.
The outer stator yoke 102 and the inner stator yoke 103 are formed such that after punching out their respective soft magnetic materials, their respective plurality of pole teeth 102a and 103a are intermeshed, with a gap. The winding 104 is formed by winding a magnet wire W around a flanged bobbin 105 made of plastic resin The flanged bobbin 105 includes a terminal block 107 protruding from its cylindrical flange substantially perpendicularly to its axial direction, and has a plurality of terminal pins 106 projecting from the terminal block 107 and fixed thereto. Lead wires of the winding 104 are hooked around the terminal pins and soldered. The terminal pins 106 are connected to a driving circuit of an apparatus on which the stepping motor is mounted.
A cutout 102b is formed in the outer stator yoke 102 in order to allow the terminal block 107 protrude outward. Referring to FIG. 12, a width of the cutout 102b is set to be substantially equal to a width of the terminal block 107, thereby securely fixing the winding 104 within coupled stator subassemblies 101 and 101.
The stator assembly 100 is formed such that the two stator subassemblies 101 and 101 each having the above-described structure are, for example, resin-molded with one another with their respective inner yokes in contact. Here, the two stator subassemblies 101 and 101 are coupled such that their respective plurality of pole teeth are misaligned by an optical electrical angle, for example, 90 degrees.
However, when the stator assembly 100 is structured as described above, a displacement in a relative electrical angle between the two kinds of pole teeth has to be adjusted, causing a dislocation between the two terminal blocks opposite to each other to occur as shown in FIG. 11. Consequently, it is difficult or complicated to make a smooth electrical connection between the stepping motor provided with the above-described stator assembly 100 and an apparatus on which the stepping motor is mounted.
For example, in case of connecting the terminal pins 106 with a flexible printed circuit (FPC) 109 having connection holes 108 as shown in FIG. 12, it is necessary to make such a special design as to boring rather big connection holes due to the dislocation between the two terminal blocks opposite to each other. However, enlarging the connection holes involves defects such as incomplete soldering, thereby diminishing the reliability of soldering.
In brief, the conventional stator assembly 100 has a defect in that the dislocation between the two terminal blocks 107 and 107 opposite to each other can occur, causing the defects of the electrical connection between the motor having the stator assembly 100 and the apparatus on which the motor is mounted, eventually diminishing the manufacturing reliability of the stator assembly and the motor.